Applicant claims priority under Rule 371 to PCT/GB00/03141, filed Aug. 14, 2000.
The present invention relates to a glass composition, particularly but not exclusively for the improved treatment and/or prevention of dental caries.
Dental caries consists of demineralization of a tooth caused by bacteria. In the early stages of caries a white spot develops on the tooth and if the disease is not halted and reversed, the enamel surface breaks down to form a lesion. This can then lead to decay and eventually, a fractured tooth. It is well known that development of dental caries may be reduced by means of various factors, such as diet and oral hygiene measures, anti-microbial treatments and the provision of fluoride to the teeth.
Current methods for administering fluoride include the fluoridation of drinking water, the ingestion of fluoride tablets, the incorporation of fluoride into mouth washes, dentifrices and foods, the topical application of fluoride solutions, gels and varnishes and recently, the incorporation of fluoride in dental materials and special devices. These have a variable effect on caries which is unpredictable on an individual basis and is dependent on patient compliance in following the prescribed regimen.
Evidence supports the concept of frequent applications of relatively low concentrations of fluoride ions for the elimination of caries. A sustained and controlled release delivery system could help to achieve this goal. At least three general approaches have been reported for the application of sustained and controlled slow releasing systems, being a sustained release ingested tablet or capsule (Masuhara et al. 1985), incorporation of fluoride in dental cements (McClean & Wilson) and an intra-oral device attached to the teeth Minth et al. 1983). However, none of these devices has proved to be suitable for use. They have either been susceptible to damage, an irritant to the mucosa or non acceptable to the patient.
Glass compositions for attaching to a tooth that release fluoride ions in the mouth to supplement dietary intake of fluoride have proved useful, where normal intake levels of fluoride are insufficient to give maximum reduction in the incidence of caries lesions in teeth.
A glass from which fluoride can be slowly leached was patented by Davidson (U.S. Pat. No. 4,920,082). The glasses described therein consist of silicon dioxide, barium oxides, aluminium oxide and fluoride in specified ranges. However, the maximum fluoride which can be retained in this system is 7% by weight and batch melting temperatures in the range of 1300–1400° C. are generally required. W088105652 also describes the preparation of novel dental composites that are claimed to release fluoride, incorporating fluorosilicate glass filters, the glass consisting essentially in weight percent of 15–50% Al2O3, 0–50% CaO, 10–65% SiO2 and 0–14% F. Again, silicate glass is known to melt at high temperatures which is unfavorable.
The use of phosphate as a glass former has been known for many years. However, the disadvantage of these glasses is that they are easily attacked by water. This property has been exploited for the development of soluble glasses for use in animal health releasing copper, cobalt and selenium to the ruminant animal over 6 to 12 months as the glass dissolves (GB Pat. No. 2116424). A more slowly dissolving glass has been used to provide copper ions in an anti-fouling paint for use on ships. This glass was formulated to dissolve over 5 years (EP App. No. 94906287.1).
Hence, the glass compositions of the prior art have not proved entirely satisfactory for supplementing the dietary intake of fluoride. The low retention of the fluoride means that the release of fluoride is not maintained over a sufficiently long period of time. The low retention would require a relatively large piece of glass to be fixed to the tooth of the patient to provide sufficient levels of fluoride release into the mouth. This would be obtrusive and reduce the appeal of the device to a patient.